<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<script>

function foo()
{
  var div = document.getElementById("div"); 
  div.appendChild(div.firstChild);
  
  var td = document.getElementById("td");
  td.setAttribute('rowspan', -2);
}

</script>

</head>

<body onload="foo()">


<div id="div"><math xmlns="http://www.w3.org/1998/Math/MathML" display="block">

    <mtable>      <mtr>         <mtd id="td"><mi>y</mi></mtd>      </mtr>    </mtable>

</math></div>

</body>

</html>
